The present disclosure relates to the subject matter disclosed in German patent application No. 100 00 954.9 of Jan. 17, 2000, the entire specification of which is incorporated herein by reference.
The invention relates to a monitoring device for checking for a predefined position of a body or for checking for the presence of a body, comprising a pivotal checking element, a motor for driving the checking element and a control device for controlling the pivotal movement of the checking element.
Monitoring devices of this type are known from DE 30 03 431 C2, DE 43 10 872 A1 or DE 196 08 628 A1.
They are employed in machine tools for example in order to check whether a tool, such as a drill for example, is still in a predefined position or, for example, has broken off, or for checking as to whether a xe2x80x9cforeign bodyxe2x80x9d has entered a region in which such a body would constitute a disturbance.
In DE 30 03 431 C2, it is proposed, for the purposes of setting the sensitivity or impact weight, on the tool or workpiece being monitored, of a sensing needle which is seated in the checking element, that the rotational speed of a dc motor and hence the pivotal speed of the sensing needle be altered.
Commencing from the state of the art, the object of the invention is to improve a monitoring device of the generic kind in such a manner that the monitoring device will be universally employable in a simple manner and in particular that damage to a body being monitored will, to a large extent, be avoidable when rapidly executing a monitoring operation.
In accordance with the invention, this object is achieved in a monitoring device of the type described hereinabove in that the checking element is adapted to be pivoted commencing from a starting position through a transition region into a monitoring region in which the predefined position of the body lies or in which the presence of a body should be monitored, and in that the control device limits the torque of the checking element in such a manner that the maximum possible torque in the monitoring region is reduced relative to that in the transition region.
By virtue of the inventive concept, it is firstly ensured that the checking element will reach the monitoring region quickly, i.e. that it can pass through the transition region with a high torque value. Secondly, in the monitoring region, the checking element will strike a body that is possibly located therein with a small amount of torque since the maximum possible torque has been reduced. The checking element will exert a force on the body even when its speed is zero i.e. it is resting on the body. By reducing the torque limit, it is ensured, in accordance with the invention, that this force will not be too large and, in particular, will not exceed a force which could destroy the body, such as a tool for example.
Account should be taken of the fact that, if the pivotal movement of the checking element is stopped by a body in the monitoring region, the control device will attempt to counteract this, i.e. the torque will be increased for a short period despite the reduction in speed. The body, on which the checking element then rests, may thereby be subjected to an increased load. Since the control process for the pivotal movement of the checking element has a certain time constant, such a short term rise in torque cannot generally be prevented. However, by virtue of the solution in accordance with the invention, whereby there is a predefined upper limit for the torque in the monitoring region, this being reduced relative to the upper limit in the transition region, the torque will be prevented from exceeding a certain value and hence the force on the body will also be prevented from exceeding a certain value.
A sensing needle is preferably arranged on the checking element. The torque will alter in correspondence with the differing lengths of the sensing needle. However, by virtue of the solution in accordance with the invention, it is always ensured that the torque will not exceed an upper limiting value independently of its actual value.
Furthermore, in accordance with the invention, provision may be made for a seal to be arranged between the checking element and the housing. A frictional moment is exerted by this seal which counteracts the torque of a shaft which is driven by the motor.
The absolute value of the torque may thereby alter in this case too. However, in accordance with the invention, it is always ensured that an upper limit for the torque will not be exceeded.
It is especially very advantageous if the motor is a dc motor and if the control device limits the supply of current to the motor. The torque, which the motor can exert, is set by the current through the motor. If the supply of current is limited, then the maximum permissible amount of torque can be set in a simple manner, and, in particular, the maximum permissible torque in the monitoring region can be correspondingly reduced by reducing the supply of current.
It is especially very expedient if the pivotal movement of the checking element is controlled by means of a combined position, speed and torque controlling. The pivotal movement can then be matched to the demands, and in particular, the transition region can be passed through quickly and the predefined position of a body in the monitoring region can be monitored without fear of damaging or even destroying the body.
It is expedient for the speed of the checking element to be reducible during its passage from the transition region into the monitoring region so as to produce the requisite control and regulation of the monitoring process in the monitoring region.
It is especially very expedient if the reduction of the torque limit is effected after the reduction in the speed of the checking element. On the one hand, it is thereby ensured that the speed of the checking element will be reduced in the monitoring region and, in particular, that the reduction of the torque limit will not prevent the speed sinking to a predefined value, but, on the other hand, it is nevertheless ensured that the checking element will not strike against a body in the monitoring region with too great a torque.
It is especially very advantageous if the control device comprises an angle transmitter. This may, in particular, be an incremental transmitter. The pivotal movement of the checking element can then be controlled in a simple manner.
It is expedient if the transition region comprises an acceleration region in which the speed of the checking element is increased commencing from the starting position. Commencing, in particular, from a static position of the checking element, this thereby permits its speed to increase rapidly so that it can pass quickly through the transition region.
Moreover, it is advantageous if the transition region comprises a braking region in which the speed of the checking element is reduced. In a simple manner, this arrangement permits the checking element to be pivoted in the monitoring region at a lower speed than in the transition region so as to prevent a hard impact between the checking element and the body that is to be monitored.
It is expedient for the speed of the checking element to be maintained substantially constant between an acceleration region and a braking region of the transition region. This thereby results in improved control and regulating possibilities since the pivotal angle is proportional to time in this region, and improved control and regulating possibilities are also created since non-linear calculations do not need to be carried out in this region whereby the adjusting behaviour for the controlled value when such controlling is required will then be improved because of the linear relationship between the pivotal angle and the time.
It is also particularly advantageous if the speed of the checking element is maintained substantially constant in the monitoring region. In essence, the reasons for this are the same as were indicated immediately above.
It is especially expedient for the control of the pivotal movement, if the control device controls the speed and torque by means of the time-dependent control of the position of the checking element. The position can be directly determined from the output of the digital angle transmitter, and since a specific pivotal angle will be turned through in specific intervals of time, the time increments can also be determined in a simple manner. By forming the corresponding quotient, the speed of the checking element can be determined to at least a first approximation. It is particularly advantageous here, if the control device defines the pivotal position of the checking element. Furthermore, it is advantageous if the control device defines the pivotal speed of the checking element.
It is especially very advantageous if the control device defines the pivotal position and the pivotal speed of the checking element. In an alternative embodiment, the control device defines the acceleration of the checking element. To this end, the speed and the position of the checking element must then be determined by means of an integration process. By virtue of the provision of the pivotal position and the corresponding time intervals, the speed is then defined, being determined, in particular, by a calculation involving the formation of quotients. The acceleration can be determined in like manner by the formation of quotients.
It is especially very advantageous if the control device is able to undergo a learning (teach in) cycle for determining the monitoring region. By virtue of such a learning cycle, it can be determined where the transition region, through which the checking element should pivot quickly, ends, and where the monitoring region, in which the torque limit is reduced, should begin. In particular, the corresponding angular values, which separate the two regions from each other, do not have to be entered directly, but the monitoring device in accordance with the invention will itself determine where the boundaries lie.
It is expedient if the monitoring region is set by the control device such that it begins at a certain angular amount prior to a body detected in the learning cycle. This angular amount may be 5xc2x0 or 10xc2x0 for example. Optimal subdivision of the whole pivotal range of the checking element can thereby be obtained, in that, it is ensured on the one hand, that the checking element will pass quickly through the transition region, and on the other hand, that accurate monitoring will be ensured in the monitoring region in which the predetermined position of the body lies or in which it should be monitored as to whether a xe2x80x9cforeign bodyxe2x80x9d is located therein.
It is expedient for stop means to be provided for limiting the pivotal movement of the checking element. An internal reference position for the monitoring device in accordance with the invention can thereby be made available and it cannot be displaced.
Expediently, for the purposes of setting a reference position of the checking element, this is moved at a predefined speed into a stop position in which corresponding stop means touch. An unaltered reference position is thereby made available.
Expediently, for the purposes of defining the reference position of the checking element in the stop position, corresponding stop means are rotated against one another at low torque. It is thereby possible, for this touching of the stops, which is necessary for defining the reference position, to be effected in a defined manner and thus allow the reference position to be precisely defined.
The monitoring device in accordance with the invention, can be employed in xe2x80x9cdifficultxe2x80x9d working conditions if a seal is arranged between the checking element and a shaft by means of which the checking element is driven.
Such an inventive seal prevents working fluids or swarf or other impurities from penetrating into the region between the shaft and the checking element and/or between the shaft and the housing. Metal swarf may, for example, become trapped between the housing and the checking element in such a manner as to hinder the rotation of the shaft. Such processes will interfere with the operation of the monitoring device i.e. it will not be able to perform its real task, checking for a predefined position of a body or checking for the presence of a body. The seal arranged in accordance with the invention will prevent metal swarf, in particular, from reaching the shaft. In addition, since an additional seal is provided, the sealing of the housing relative to the exterior space will be improved. The monitoring device in accordance with the invention will thereby be less susceptible to disturbances and the downtime, in which the operation of the monitoring device is interrupted and hence it can no longer perform its real task, will be much reduced. Moreover, metal swarf can perforate the shaft passage seal in the housing so that fluids may enter into the interior of the housing. The additional seal provided in accordance with the invention completely prevents metal swarf from reaching the shaft seal.
It is particularly very advantageous if the seal abuts the checking element and abuts the housing. The intrusion of swarf and/or fluids into the region between the checking element and the shaft and/or between the housing and the shaft is thereby prevented.
It is advantageous for the seal to be formed symmetrically about an axis and especially about a rotational axis of the shaft. A substantially angle-independent frictional moment can thereby be obtained, especially during the rotational movement of the checking element, thereby achieving simpler control of the pivotal movement of the checking element.
It is particularly very expedient if the seal is seated between the checking element and the housing co-axially relative to the shaft.
It is expedient for an intermediate space to be formed between the shaft and the seal. Consequently, the seal itself does not abut on the shaft and will not hinder its rotational movement.
In an advantageous variant of an embodiment, provision is made for the seal to be rotationally fixed relative to the checking element. The seal is thus carried along by the checking element during the pivotal movement of the checking element whilst it will rotate relative to the housing. Basically, it is also conceivable for the seal to be rotationally fixed relative to the housing and then to rotate the checking element relative to the seal. However, the proposed variant is more expedient from a constructional point of view since a seal must be provided around the shaft in the housing in order to seal the passage for the shaft through the housing. The corresponding annular space is not available for the arrangement of a mounting element for the seal between the checking element and the housing. By contrast, a further seal for the checking element itself does not need to be provided apart from the seal between the checking element and the housing.
Expediently, the checking element comprises a mounting element for the seal onto which the latter is adapted to be put in order to fix it non-rotationally relative to the checking element. An easily manufacturable, easily releasable but nevertheless sealed connection between the seal and the checking element in accordance with the invention can thereby be achieved in a simple manner.
From a manufacturing point of view it is particularly expedient if the mounting element is formed by a mounting ring through which the shaft is guided and onto which the seal is adapted to be put. The seal can thereby be arranged completely around the shaft in a simple manner.
Furthermore, it is expedient to provide an annular recess for accommodating the seal between the mounting element and the checking element. An abutment face for an end-face of the seal is made available by such an annular recess, and in addition, the seal can rest in full area contact on an outer surface of the mounting ring. The seal is thus connected to a large surface area of the checking element so that a good sealing effect is thereby achieved.
Expediently, an outer diameter of the seal substantially corresponds to the diameter of the checking element so that, firstly, a large abutment face for the seal is available on the checking element and secondly, material will not be wasted unnecessarily.
It is particularly very expedient if the seal comprises a packing ring for the purposes of putting it onto the checking element. Good sealing properties between the seal and the checking element are achieved by virtue of such a packing ring.
Furthermore, it is particularly very advantageous if the seal comprises a collar having a V-shaped sealing lip which abuts the housing. Good sealing properties are achieved between the seal and the housing by virtue of such a sealing lip, and the spacing between the checking element and the housing can be varied by means of the sealing lip without the need to provide a plurality of seals for this purpose, since, to a certain extent, the V-shaped sealing lip allows the axial extent with reference to the direction of the rotational axis to be set.
It is expedient if the collar is rotatable with the checking element relative to the housing.
In order to obtain good sealing properties between the seal and the housing on the one hand, and in order to be able to vary the spacing between the checking element and the housing on the other, it is advantageous if the outer surface of the collar is substantially in the form of a truncated cone at least when force is not being applied thereto in the axial direction. An imaginary cone peak of the V-shaped collar then points towards the checking element. Thus, when the axial spacing between the checking element and the housing becomes smaller, the collar can spread in a radial direction so that the effectiveness of the seal will not worsen despite the change in this spacing.
It is expedient if the inner surface of the collar is in the form of a truncated cone at least when force is not being applied thereto in the axial direction. This ensures that the sealing lip will be in full area contact with the housing even when the spacing between the checking element and the housing becomes smaller thereby achieving good sealing properties.
It is expedient if an axial extent of the seal can be varied by the collar so that the monitoring device in accordance with the invention can be employed in variable manners and is particularly economical.
Further features and advantages of the invention form the subject matter of the following description taken in conjunction with the sketched illustration of the embodiment.